This specification relates to systems and techniques for thermal transfer printing.
Thermal transfer printing involves the use of a ribbon to carry a material (e.g., ink) to the location of a printhead, where heat is then used to transfer the material from the ribbon to a substrate (e.g., paper or plastic). Many different variations of this general process have been developed over the last sixty years, and various improvements have also been made in the configurations and control systems employed for thermal transfer printers. For example, U.S. Patent Pub. No. 2013/0039685, now U.S. Pat. No. 9,340,052, describes a motor control system, a method of operating a motor control system, a tape drive including a motor control system, a method of operating such a tape drive, and a printing apparatus including such a tape drive, as can be used with thermal transfer printing.
In spool-to-spool printers, ink is supplied in ribbon form rolled onto cores, which are mounted or pressed onto spools (a supply spool and a take-up spool) in the printer. The movement of the spools can be precisely controlled by an electric motor for each spool. During a standard print operation, the motors are controlled to move the ribbon in front of the printhead at the same speed as the substrate where ink is removed from the ribbon. In order not to waste ribbon, each print should land on the ribbon directly adjacent to the previous print. This typically requires backing up the ribbon between each print in order to allow enough space on the ribbon to accelerate the ribbon to match the substrate speed before printing. For each print, both motors are used to accelerate the ribbon to the substrate speed, move the ribbon forward at the print speed, decelerate to zero velocity, accelerate in the reverse direction, stop and then decelerate again in the reverse direction, stop and then start the entire process over again for the next print. All of this is often complicated by the fact that the diameters of both spools are changing as the supply side is used up and the take-up side grows. Similar limitations apply to traditional shuttled printers, where the pack rate is limited by the operations of the shuttle, which goes back and forth for each print, and the length of the print may be limited by the travel distance of the shuttle.